How to create a sys_file_reference inside another sys_file_reference? - typo3

Question

I need to add some track files to a TYPO3 file reference. So I extended the TCA for sys_file_reference and added some fields. One of the fields should be a reference to another file.
It works as far that I can chose a file in the backend
Unfortunately, I can't save if I have a track added. TYPO3 throws me an exception.
#1300098528 InvalidArgumentException Incorrect reference to original file given for FileReference.
This exceptions happens because uid_local of the track reference is 0. But I don't know why this is 0 and how to fix it.
This is my TCA Configuration
'tx_eos_video_tracks' => [
'exclude' => 1,
'label' => 'Track files',
'description' => 'captions, chapters, descriptions, metadata, subtitles',
'config' => \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::getFileFieldTCAConfig('tx_eos_video_tracks', [
'appearance' => [
'createNewRelationLinkTitle' => 'Add Track'
],
'overrideChildTca' => [
'types' => [
'0' => [
'showitem' => '
--palette--;;tx_eos_video_tracks_palette'
]
],
],
], 'vtt,srt')
],

Answer 1

Ok, I found the Solution. There must be always the fields uid_local, hidden, sys_language_uid, l10n_parent in the Child TCA.
There is a predefined palette ('filePalette') which adds the fields without showing them to the user.
So Changing
'overrideChildTca' => [
'types' => [
'0' => [
'showitem' => '
--palette--;;tx_eos_video_tracks_palette'
]
],
],
to
'overrideChildTca' => [
'types' => [
'0' => [
'showitem' => '
--palette--;;tx_eos_video_tracks_palette,
--palette--;;filePalette'
]
],
],
resolves my Issue